M.F. Selekwa and E.G. Collins, Jr
Loop-shaping design, fuzzy logic, constrained optimization
The H∞ loop-shaping design method is an effective way to design robust controllers. One of the main limitations in the design of H∞ loop-shaping controllers is that the design method concerns frequency domain specifications that do not precisely represent the underlying time domain performance requirements. Even if the time response constraints were not present, the approach is based on trial-and-error selection of the frequency-dependent weights that are used in the design. Selection of these weights becomes more diffcult if time response constraints must be satisfied. This paper presents a systematic way of selecting the loop parameters for the frequency-dependent weights, and develops a fuzzy algorithm that selects these parameters so that the resulting H∞ loop-shaping controller yields a closed-loop system that satisfies the time response constraints for a linear single-input single-output (SISO) system. It is seen that although most of the time response characteristics of the system can be improved by changing any of the loop parameters, the frequency domain constraints normally set limits on some of these loop parameters in such a way that the latter cannot be changed further to improve the time response characteristics of the system.
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